DE 198 28 368 C2 discloses a process for operating two-stage or more than two-stage compressors, in which each compressor stage has a separate surge limit control valve arranged between a delivery line via a blow-by line and an intake line. The surge limit control valve blows off into the intake line of the corresponding compressor stage. Furthermore, a flow computer for computing the intake flow as well as a computer for the minimum allowable desired flow, which is determined from the end pressure or the delivery head, are provided.
Furthermore, EP 0 810 358 A2 discloses a process for controlling gas pressures of a regenerator with a gas expansion turbine in the flue gas line with a generator, wherein a process controller opens the inlet fittings of a gas expansion turbine and/or the bypass fittings or throttles the bypass fittings. A plurality of resolver transmitters, which preset the manipulated variables for the downstream fittings, are arranged downstream of the process controllers.
Moreover, DE 100 12 380 A1 discloses a process for protecting a turbocompressor with the downstream process from operation in the unstable working range, wherein a machine controller is used, which optionally has a suction pressure controller, an end pressure controller and a bypass controller, besides a surge limiter. A control matrix is determined from the position of a control unit that determines the flow to the process, optionally taking into account additional influencing variables, such as the compressor suction pressure and the compressor outlet pressure and the compressor suction temperature as well as the process pressure. Based on the control matrix, the necessary position of the surge limit control valve as well as of the bypass valve, of the suction pressure control valve and of the actuating drive is determined directly for the compressor inlet blades in the case of a rapid transient change in the working point. The actuating variable determined is then sent directly as a manipulated variable to the surge limit control valve, the suction pressure controller, the end pressure controller and the bypass controller.
Furthermore, EP 0 757 180 B1 discloses a process for avoiding controller instabilities in surge limit controls for protecting a turbocompressor from surging if the proportional sensitivity of the surge limiter was selected to be too high by means of blow-off via a blow-off valve. The speed with which the blow-off valve closes over time takes place is controlled by means of an asymmetric gradient limiter, with no time limitation being effective in the opening direction. However, a parametrizable time limitation of the closing operation of the blow-off valve is provided in the closing direction.
It is assumed in the prior-art processes that the position of the surge limit in the performance characteristic of the compressor is known. The coordinates of the working point are usually plotted in the performance characteristic as compression work or enthalpy difference or delivery head as a function of the suction volume flow. The parameters of the particular variables must be known as well.